1. Field of the Invention
The present invention relates to an ergonomic apparatus for supporting the human arm during manual operations so as to counterbalance at least a part of its weight and reduce the strain on supporting muscles and tendons.
More specifically, the invention is particularly, although not exclusively intended for ultrasonic diagnostic operations and aims at providing a simple, esthetical and practical solution to the increasing problem of fatigue and pain caused to operators by the repetitive manipulation of the ultrasonic probe in a position where the operator's arm is usually extended far from his body, thus causing a high solicitation at the biceps and shoulder level. Effectively, many current medical applications of ultrasonic diagnostic, such as in obstetrics, require intensive manipulation of the probe around the patient's tissues and obstacles to obtain images as good as possible or track moving targets. Therefore, operators' arms are much solicited causing pain, disease, low productivity, absenteeism, that induce both human and economic costs.
Although the invention will be described in detail with respect to the latter field of application, it shall be understood that it might be used in many other fields such as assembly, physiotherapy and assistance to persons affected by a restriction of arm mobility.
2. Brief Description of the Prior Art
A few solutions to the problem of holding an ultrasonic probe have been proposed in the past and they all suffer from major drawbacks. Namely, all of them are designed to hold the probe itself and provide no assistance to the operator for supporting the weight of his own arm acting in cantilever and causing an important torque to be counterbalanced by the effort of the arm and shoulder muscles and tendons. Such a mechanism is disclosed in U.S. Pat. No. 5,348,014 (Okado) issued on Sep. 20, 1994, which describes an overhead arm mechanism provided with a constant force spring counterbalanced wire to which the probe is suspended. Considering that most contemporary probes are much lighter than the operators arm, supporting the probe alone provides very limited relief of the physical stress to be supported by the operator. Even if the winding force of the wire was increased to account for the arm weight, the point of application of the compensating force would not be adequate and added stress in the wrist and no significant comfort improvement if any would yield. Moreover, that support is limited in mobility and positioning flexibility since it is fixed to the ultrasonic apparatus body and does not provide operator adjustable counterbalancing force.
U.S. Pat. No. 5,279,486 (Harmon) issued on Jan. 18, 1994 discloses a medical support using an horizontal arm to support a wire through two pulleys. One end of the wire supports a medical apparatus while a counterweight is attached to the other end of the wire and counterbalances the weight of the apparatus. That concept with limited number of degrees of freedom is only appropriate for static support of an apparatus and do not feature practical adjustment of the counterbalancing force as required for supporting the arm in different positions and providing optimal comfort to different operators.
U.S. Pat. No. 4,548,374 (Thompson et al.) and U.S. Pat. No. 4,241,891 (Rudolph) respectively issued on Oct. 22, 1985 and on Dec. 30, 1980, provide even worse solutions for supporting the probe, since the weight of most of the articulated supporting arm is balanced by a counterweight located near the base. These concepts result in sturdy and heavy structures which present a high level of friction and inertia that would prevent utilisation as a human arm support since freedom of movement would be too much affected.
Many arm supports are referenced in the prior art, but they are all intended to relief stress and pain experienced by keyboard operators. These systems, for example the system described in U.S. Pat. No. 5,074,501 (Holtta) issued on Dec. 24, 1991, support the operator's arm from underneath and provide no supported or balanced mobility over a three dimensional work envelope, and therefore would not comply with an application requiring such a level of freedom as for ultrasonic diagnostic apparatus operators, assembly tasks, restrained mobility persons or like applications.